How to connect back outlet toilet to cast iron soil stack?

I have a back outlet, floor mount toilet that leaked behind the wall. When I removed drywall, I saw that the connection between cast iron soil stack and the plastic connector is leaking. Please see photos.

What is the proper way to connect the cast iron and plastic? Should I remove and replace the plastic connector, or leave it in place and seal it somehow. The plastic connector is threaded, but I doubt that cast iron has a thread. (I have not tried taking this connection apart.)

My other question is how to properly connect the toilet. A wax ring was used, but the toilet was leaking there as well. I read that a wax ring is not suitable for rear discharge toilet.

Thank you for advice.

regular wax ring or a http://www.supplyhouse.com/Sani-Seal-BX01-Sani-Seal-Waxless-Toilet-Gasket

frodo said:

regular wax ring or a http://www.supplyhouse.com/Sani-Seal-BX01-Sani-Seal-Waxless-Toilet-Gasket

Click to expand...

Thank you. So this is for connection between the toilet and the plastic connector that goes to the stack. What about the connection between the cast iron stack and the plastic part.

I think this is what I have. What is the proper way to connect it to cast iron stack?

https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dindustrial&field-keywords=Sch+80+Threaded+Nipple+890-040

not understanding your question

the nipple screws into the carrier, use pipe dope, or the black crap that comes with nipple

the wax ring goes in between the bowl and nipple

the bolts hold it tight


the nipple, should stick out proud from the finished wall by 1/4''

did that answer your question ?


if you are using a new, plastic factor nipple, they make a tool to tighten it with
you can make the tool yourself using a 1x1 angle iron and a grinder

Thank you, frodo. I think I am getting it now. The nipple did stick out about 1/2" from the finished wall.

The leak is between the carrier and the nipple, so it sounds like I have to unscrew the nipple, and re-seal it with pipe dope. Any specific product you recommend?

Also, what would be a good tool to unscrew the nipple? I tried this strap wrench, but could not move it at all because the strap slips.

https://www.menards.com/main/plumbing/rough-plumbing/pipe-tubing-hoses-fittings-accessories/plumbing-tools/plumbing-hand-tools/plumbing-wrenches-tool-kits-tool-bags/plumbworks-11-strap-wrench/p-1444433583382-c-8615.htm?tid=829149024062349055

I have sprayed it with Liquid Wrench lubricant and will try again, but maybe you can suggest a better approach.

Are you sure it's leaking between the nipple and the cast iron and not from the wax seal? It would take a very loose nipple for it to leak.

The wax seal definitely leaked, but it looks like the larger leak was inside the wall. Unless the water was coming from the wax seal and along the outside of the nipple. The nipple is definitely not loose. I cannot unscrew it, so it does seem counter intuitive that it would leak.

Attached are more pictures. Do you think the rust on the cast iron is coming from the wax seal leak rather than from the threaded connection?

Here's a larger photo of the rust spot. Does this suggest a leak in the threaded connection, or is water coming outside the plastic pipe from the broken wax seal?

test it, remove the pipe above the carrier, fish a blow up ball into the carrier

fill with water and look at the nipple.

to remove the nipple. use a 48'' pipe wrench

i have..not saying this will work for you

removed the nipple using a 24'' pipe wrench turned sideways , this will destroy the threads, have another nipple ready to use

put the wrench on the pipe, tighten it. then pull sideways. the bind will catch,

position the wrench so you can put your foot on it and stomp/kick/ te wrench in a down ward motion
breaking the nipple loose

I outta charge you for my tricks !!!!!!!!!!!!!!!!

Thank you. I am hesitant to remove the pipe above the carrier because it goes to the apartment above. I was hoping I could disassemble without damaging the nipple, but this makes sense.

Would these ABS nipple and coupling work for me?

0100N08P 4x8-1/4 ABS NIPPLE
https://www.zoro.com/jay-r-smith-mfg-co-nipple-4-in-x-8-14-in-0100n08p/i/G0700126/

0100C-P ABS ADJUSTING COUPLING
https://www.zoro.com/jay-r-smith-mfg-co-coupling-abs-plastic-0100c-p/i/G0700150/

0100GASKET-NEOP Neoprene Outlet Gasket
https://www.zoro.com/jay-r-smith-mfg-co-gasket-water-closet-0100gasket-neop/i/G6168662/

that will work